Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is supplied in a continuous coiled configuration, designed to meet the demanding requirements of heat exchange, fluid transport, and thermal management systems across multiple industrial sectors. The coil form factor offers superior material utilization, reduced fabrication waste, and enhanced production efficiency compared to straight-length tube alternatives.
The Coiltube product line is particularly distinguished by its application in Fan Coil Units (FCUs) with mixed-air functionality, where the tube geometry and material properties directly influence the thermal performance, energy efficiency, and service life of HVAC (Heating, Ventilation, and Air Conditioning) systems. The coiled configuration enables compact heat exchanger assembly, optimized airflow distribution, and improved heat transfer coefficients through controlled coil pitch and diameter tolerances.
2. Material & Properties
The Coiltube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, mechanical strength, and thermal conductivity. The following material grades are available:
- AISI 304 (UNS S30400) — General-purpose grade with excellent corrosion resistance in most atmospheric and chemical environments; Chromium (Cr) content of 18–20%, Nickel (Ni) content of 8–10.5%.
- AISI 316 (UNS S31600) — Enhanced corrosion resistance with Molybdenum (Mo) addition (2–3%); suitable for marine, chemical processing, and aggressive environments.
- AISI 321 (UNS S32100) — Titanium-stabilized grade for elevated temperature service; resistant to intergranular corrosion.
- AISI 316L (UNS S31603) — Low-carbon variant of 316 for welding-intensive applications; Carbon (C) content ≤ 0.03%.
Key Mechanical and Physical Properties (AISI 304 Reference)
- Tensile Strength: ≥ 520 MPa (75,400 psi)
- Yield Strength: ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Thermal Conductivity: 16.3 W/(m·K) at 25°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (10–100°C)
- Density: 8.0 g/cm³
- Maximum Service Temperature: 870°C (in air)
3. Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 38.1 mm (¼" – 1½") | ±0.05 mm |
| Wall Thickness | 0.5 mm – 3.0 mm | ±10% |
| Coil Inner Diameter (Coil ID) | 500 mm – 1500 mm | ±20 mm |
| Coil Length (per coil) | 50 m – 500 m | ±5% |
| Surface Finish | 2B, BA (Bright Annealed), No. 4 Brushed | Per ASTM A473 |
| Surface Roughness (Ra) | 0.4 – 1.6 µm (BA finish) | — |
| Coil Pitch | 1.5× OD – 5× OD (configurable) | ±0.5 mm |
| End Condition | Plain end, Beveled end, or Threaded (NPT/BSP) | Per drawing |
| Applicable Standards | ASTM A213, ASTM A269, ASME B36.19M, EN 10216-5 | — |
| Pressure Rating | Up to 16 bar (PN16) depending on OD and wall thickness | Per EN ISO 4414 |
4. Manufacturing Process
The production of the Stainless Steel Coiltube follows a rigorous multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Cold-rolled stainless steel strip is procured from certified mill sources, with each batch accompanied by a Mill Test Certificate (MTC) verifying chemical composition and mechanical properties.
- Slitting and Leveling: The strip is slit to the precise width required for the target tube OD, followed by precision leveling to eliminate residual stresses and ensure flatness tolerances of ±0.1 mm/m.
- Forming (Roll Forming): The leveled strip passes through a series of progressive forming rolls that gradually shape the strip into a tubular cross-section. The forming tooling is designed with tight tolerances to minimize cross-sectional distortion.
- Seam Welding: A high-frequency induction welding (HF) process is employed to create a hermetic longitudinal seam. The welding parameters (frequency, power, roll pressure) are optimized for each OD and wall thickness combination to achieve full penetration welds with minimal heat-affected zone (HAZ).
- In-line Inspection: The weld seam is inspected using eddy current testing (ECT) and/or ultrasonic testing (UT) to detect porosity, lack of fusion, and geometric defects. Non-conforming sections are automatically marked and removed.
- Heat Treatment (Annealing):strong> Where required, the tube undergoes solution annealing at 1050°C – 1150°C followed by controlled cooling to restore full austenitic microstructure, relieve residual stresses, and achieve the required mechanical properties.
- Precision Coiling: The finished tube is wound onto a coiler at controlled tension to produce a uniform, non-deformed coil. Coil pitch and turn-to-turn spacing are maintained within specified tolerances to facilitate downstream heat exchanger assembly.
- Final Inspection and Packaging: Each coil undergoes dimensional verification, surface inspection, and pressure testing (100% pneumatic or 10% hydrostatic sampling). Coils are protected with anti-corrosion wrapping, edge protectors, and wooden or steel pallets for shipment.
5. Applications
The Coiltube product is engineered for use in the following application domains:
5.1 HVAC Systems — Fan Coil Units (FCU)
The primary application of this Coiltube product lies in the construction of air-side heat exchangers within Fan Coil Units, particularly those incorporating mixed-air (fresh air + recirculated air) functionality. The coil tube serves as the refrigerant or hot water circuit within the FCU's heat exchanger core, facilitating efficient thermal exchange between the working fluid and the airstream. Key performance considerations include:
- Optimized coil pitch for balancing pressure drop and heat transfer area
- Corrosion resistance to resist condensation-induced degradation in humid indoor environments
- Dimensional consistency to ensure proper fin-to-tube expansion fit during heat exchanger assembly
- Compatibility with mixed-air configurations where variable humidity and temperature conditions demand robust material performance
5.2 Additional Applications
- Food and Beverage Processing: Sanitary-grade coil tubes for pasteurization, sterilization, and beverage dispensing systems (316L grade).
- Chemical Processing: Corrosion-resistant coil tubing for chemical dosing, sampling, and process control lines.
- Pharmaceutical Manufacturing: Hygienic coil tubing meeting FDA and EHEDG standards for CIP (Clean-in-Place) systems.
- Automotive and Aerospace: Precision coil tubing for fuel systems, hydraulic circuits, and thermal management.
- Oil and Gas: Subsea and surface coil tubing for well intervention and production systems.
- Electronics Cooling: Compact coil heat exchangers for server rooms, data centers, and power electronics.
6. Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product reliability and regulatory compliance:
- ISO 9001:2015 — Quality Management Systems certification covering design, manufacturing, and service processes.
- ISO 14001:2015 — Environmental Management Systems certification for sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
- CE Marking — Compliance with European Directive 2014/68/EU (Pressure Equipment Directive) for pressure-rated applications.
- EN 10204 3.1 — Material Test Certificates issued by authorized inspection personnel for each production batch.
- ASME Stamp (PN) — Pressure Vessel and Piping certification for applicable product configurations.
- NSF/ANSI 61 — Drinking water system component certification (for 316L sanitary grade applications).
7. Unique Selling Points
- Application-Optimized Design: Coiltube geometry specifically engineered for Fan Coil Unit heat exchanger integration, with validated coil pitch and diameter combinations that maximize heat transfer efficiency (U-value) while minimizing fan power consumption — directly addressing the energy efficiency challenges identified in mixed-air FCU system research.
- Superior Corrosion Resistance: Austenitic stainless steel construction provides resistance to condensation corrosion, chlorides, and organic acids commonly encountered in HVAC environments, extending service life beyond carbon steel alternatives by a factor of 5–10×.
- Dimensional Precision: Tight OD and wall thickness tolerances (±0.05 mm) ensure reliable mechanical expansion of aluminum fins onto the tube surface, producing consistent heat exchanger performance coil-to-coil.
- Full Traceability: Each coil is assigned a unique heat number and batch identifier, enabling complete material traceability from mill origin through final product delivery.
- Customizable Configurations: Flexible manufacturing capability accommodates a wide range of OD, wall thickness, coil diameter, and surface finish requirements to meet specific OEM specifications.
- Cost-Effective Coil Delivery: Continuous coil format reduces cutting losses by up to 15% compared to straight-length tube, offering significant material cost savings for high-volume heat exchanger manufacturers.
Technical Note: The application of stainless steel coil tubes in Fan Coil Units with mixed-air functionality represents a critical interface between material science and thermofluids engineering. As demonstrated in applied research on mixed-air FCU systems, the tube material's corrosion resistance under variable humidity conditions, combined with the geometric efficiency of coil configurations, directly impacts the seasonal energy efficiency ratio (SEER) and coefficient of performance (COP) of the complete HVAC system. Wenzhou Jixing Metal Materials Co., Ltd. leverages deep domain expertise to deliver coil tube products that are fully optimized for these performance-critical applications.